The epitaxial layers suitable for field effect transistors (FET) and transferred electron (TED) Gunn effect devices must contain very few lattice imperfections because crystalline lattice imperfections reduce their electron mobilities and the latter represent one of the principal figures of merit of FET and TED. This can be achieved only if the lattice constant of the epitaxial layers are matched to better than 0.1% to their substrates. A further requirement is that these substrates be semi-insulating so as to prevent short circuiting of the active devices or parasitic coupling between them or other circuit elements. The best semi-insulating InP presently available is not satisfactory; its resistivity in some three to four orders of magnitude smaller than that of semi-insulating galium arsenide GaAs. It would then be desirable to deposit or grow InP layers epitaxially on semi-insulating GaAs. Semi-insulating GaAs and InP have different lattice constants. The lattice constant mismatch between them is 3.89%. Semi-insulating InP cost is considerably more costly than semi-insulating GaAs and is not readily available.